Power hammer



Aug. 24, 1948. R. WORTH 2,447,386

POWER HAMMER Filed Oct. 11, 1945 3 Sheets-Sheet 1 INVENTOR.

ROBERT WORTH R. WORTH POWER HAMMER Aug. 24, 1948.

5 Sheets-Sheet 2 Filed Oct. 11, 1945 a 3 a m a 6 w M 9 6 m 2 6 7 w 6 1 m M 7 WW 2 5 I 2 8 2M 2 6 a, 9 4a 6 M J H |||+||l|| Mal I 1 V. 1% W. 4 3 W y y .fi wC z Aug. 24, 1948. WORTH 2,447,886

POWER HAMMER Filed Oct. 11, 1945 3 Sheets-Sheet 3 INVENTOR g; a a ROBERT WORTH BY 7 a Mfimm b m ATT'ORNEY Patented Aug. 24, 1948 POWER HAMMER norm Worth, Nutlcy, N. 1., aaaignor to Homelite Corporation, East Port Chester, Conn., a corporation of Connecticut Application October 11, 1945,, Serial No. 621,798 '10 Claims. (01. 125-33) This invention relates generally to impact devices as embodied for example in power hammers used for pavement breaking, rock drilling. Pile driving, riveting or the like, hereinafter referred to generically as powerhammers.

Where heavy hammering operations are required such as those in connection with the breaking of pavements, excavating, riveting, cutting, drilling and the like, it is desirable that a tool be used which is relatively light in weight in proportion to the power delivered, easily maneuverable, and highly portable.

Power hammers have been operated in the past by pneumatic pressure, directly driven by internal combustion engines, or by electrically powered means. The air driven hammers have a number of disadvantages including the requirement of expensive and bulky compressor equipment, clumsy air pressure lines communicating from the compressor to the tool, and relatively low efliciency since, in order to get an eifective blow, compressed air tools must apply full air pressure through the entire stroke of the piston, discharging the only partially used air, still under pressure, at the end of the stroke.

Presently available power hammers which are driven by self-contained internal combustion engines have the disadvantges of fire hazard, discomfort for the operator in warm weather, hard starting, erratic operation under changing conditions, andhigh maintenance cost owing to the high wear produced in this type of mechanism. Further, they are heavy and bulky for the power delivered.

In electrically driven power hammers,the rotary motion of an electric motor is converted into reciprocatory movement of an impact or striking element. While electrically operated hammers have many advantages over air driven hammers and those driven directly by internal combustion engines, the electric hammers heretofore available have been open to the objection of relative low operating eiiiciency. This has resulted in the hammer being ineflective for the intended work or alternatively in the need for such a large electric motor as to render the device heavy and clumsy to handle and expensive to operate. Moreover, previous electrically driven devices of this class have required frequent servicing and repair owing to the utilization of packings, elastic elements and other parts subject to wear and fatigue and have been subject to the further disadvantage that shock from the impact element is transmitted back to the motor and driving mechanism with deleterious results. While the problems of overcoming these objections have long existed and many attempts have been made to solve them, no satisfactory solution has heretofore been found.

' It is an object of the present invention to overcome the disadvantages of the prior art devices and provide a power driven hammer of superior performance and operating at a relatively high efliciency. The high efliciency attained by the arrangement of parts and cycle of operation in converting the rotary motion of the motor into r'eciprocatory motion of an impact element in accordance with the invention results in delivering an impact of maximum effectiveness. The effectiveness of the impact is increased by the fact that energy is stored substantially throughout the cycle so as to utilize the continuous power output of the motor and full use is made of this stored energy in the delivery of the blow.

The present invention thus makes possible the construction of a heavy duty hammer that is relatively light weight and compact in size. Moreover, the construction and cycle of operation in accordance with the invention results in cooler running and in longer life with a minimum of servicing or repair. A further advantage of the inventionis that the transmission of shock back into the operating parts and structure of the hammer is minimized. This not only contributes to the long life of the hammer and freedom from mechanical failure but also reduces operator fatigue.

These and other objects and advantages of the invention will appear more fully from the following description and claims and from the accompanying drawings which show by way of example an embodiment selected to illustrate my invention.

In the drawings:

Fig. 1 is a front elevational view of a power hammer showing an embodiment of the invention in which an electric motor is used as a power source.

Fig. 2 is a longitudinal sectional view as seen from the plane 2-4 on Fig. 1.

Fig. 3 is a sectional view as'seen from the plane 3-4 on Fig, 2.

Fig. 4 is a schematic view showing the position of the parts through a cycle of operation of the hammer.

'I'heembodiment of my invention illustrated in the drawings includes a main casing or housing II, a removable cover plate I2, a driving motor II, a counter-shaft H, a connectingrod ii, a piston I, a cylinder i1 and a front head ll.

The front head i3 is adapted to maintain any suitable tool bit such as the tool bit i8, in a position to be struck by the ram head 28 on the lower or work end 2| of the cylinder |1. As best seen in Fig. 1 the tool l3 may be provided with a collar 22 by means of which it is maintained against the lower or outer end 22 of the front head l8 by the use of the spring retainer 23 in a well known manner. The front head l3 may be connected in any suitable manner as by the springs and bolts 24 to the lower or work end 28 of the 23 and 23 are the ledges 3| and 32 supported by ribs 33. The ribs 33 not only serve to maintain the ledges 3| and 32 in alignment with respect reciprocated longitudinally of the casing II by the connecting rod l8, one end 83 of which en-- gages said pin and the other end 83 of which engages a wrist pin or stud 81 mounted eccentrically of the countershaft l4. The countershaft is journalled by bearings 88 and 8| in a housing portion 82 of the cover plate l2 and access thereto may be gained through a removable cover 83. The inner end of the countershaft H has secured thereto a gear 84 which carries the aforementioned stud 81.

The driving motor i3 is preferably of an induction type electric motor running at a substanplate |2. 'The motor shaft 88 may carry a fanto each'other, but also reenforce the wall 34. A

able manner as for example by the use of the bolts 31 and 33 which extend through openings in the tracks and screw into threaded holes in the ledges 3|, 32. The tracks 38, 38 engage grooves 4| provided in the opposite sides of the cylinder l1 to support the cylinder forreciprocation in a lengthwise direction. The cylinder is removable from the casing II by removing the front head l8, or by removing one or both of the tracks 38, 38.

The cylinder I1 is closed at its inner or upper end 38, preferably by a threaded plug 48, and is closed at its lower or work end by the ram head 28. Substantially midway of the length of the cylinder, that is to say midway of the hollow portion thereof, the cylinder is provided with an opening 42 and an elongated slot 43. The slot 43 is preferably substantially equal to or' slightly greater than the length of the piston l8. As seen in Fig. 2, the opening 42 is diametrically opposite the pin 43 is detachably secured endwise in the opening 48 by a screwand circular wedge or cone structure generally indicated by reference char- 'acter 43. The screw engages a correspondingly threaded hole in the end of the pin 43, and the head of-the screw, which may be hexagonal as shown, is accessible through the opening 42 when the piston is in its midway position and through an opening 83 in the wall .34 of the casing II when the detachable cover plate 88 is removed. The cover plate 88 may be maintained in position in the circular rabbet 8| in any suitable manner as by the use of screws 82 which engage threaded holes in said rabbet. The bolt 43 is brought from the position shown in Fig. 2 into juxtaposition with the opening 83 by rotation of the countershaft |'4 through part of a revolliflOfL The opposite end 84 of the pin 43 is disposed within a cross head 88 mounted for slidable reciprocationin a guide 88 which is secured to the inner surface of the cover plate |2. 'llhe pin 43,

and hence the cross head 88 and piston I8. are

31 which serves to cool the motor and at the inner end of said shaft a pinion 88 is provided. The pinion 83 meshes with the gear 84 on the countershaft l4. The motor bearings, the bearings 8| and 82 of the countershaft and the connecting rod bearings, may be of the ball type as shown. The cover plate carrying the motor and the countershaft and gear 84 is maintained in position by a series of bolts 88 which engage corresponding portions of the casing H and particularly the walls 28, 21, 28 and 18.

Lubrication may be supplied to the operating parts in the chamber 1| inside the casing II by of the tool l8 and the piston |8 is at the bottom of its stroke. When the blow is struck, the cylinder |1 rebounds from the tool I3 and its upward motion is assisted by the fact that the connecting rod i8 has begun to pull the piston upwardly as shown at -B in Fig. 4. This upward movement of the piston causes the upper end of the piston to move past the upper end 18 of the slot 43 in the cylinder so thatthe upper chamber 3| of the cylinder is hermetically sealed. Movement of the lower end of the piston upwardly past the lower end 18 of the slot 33 permits air at atmospheric pressure to enter the chamber 38 in the lower portion of the cylinder. At 0- in-Fig. 4 the upward movement of the piston 18 and cylinder |'1 continues as indicated respectively by the arrows X and Y. As the gear 84 is driven at substantially constant speed the movement of the piston I8 is approximately sinusoidal so that the piston is accelerated during its movement from the position shown at A in Fig. 4 to the position shown at D. The cylinder i1 is also being accelerated in its upward movement but because of its inertia it is accelerated less rapidly than the piston so that the air in chamber 3| is progresslvely compressed.

At 12 in Fig. 4 the piston has begun to decelerate while the cylinder continues to accelerate so that the two are moving upwardly at approximately the same speed. The air in chamber 8| is maintained under compression and may be slightly more compressed at E than at D. The deceleration of the piston continues at F and the air that has been compressed in chamber 3| now begins to expand to cause the upward movement and acceleration of the cylinder I! to continue. At G the stud 51 has travelled through substantially 180 and the piston l8 has reached the top of its stroke, but the cylinder l1 continues to move upwardly.

The piston now begins to move downwardly as indicated at H while the inertia of the cylinder causes it to continue to move upwardly, the limit of its upward movement being reached approximately at the position shown at I in Fig. 4. 'It will be noted that during the phases shown at H and I the cylinder and piston are moving in opposite directions. At approximately the position shown at H the piston closes the port at the lower end 18 of the slot 43 in the cylinder and begins to compress the air in the chamber 80 while the upper chamber 8| is opened to atmospheric pressure. Maximum compression in the chamber 88 occurs approximately at J where the piston has reached its greatest speed of movement in the direction of the tool i9. Between J and K the cylinder and piston move substantially together so that the air in chamber 88 is maintained under high compression and the-driving force of the rapidly moving piston is transmitted through this compressed air to the cylinder. At'L the piston is slowing down but the air under compression in chamber 80 forces the cylinder to travel at still greater speed in the direction of the tool i9 and increases the momentum which the cylinder already has. The cylinder attains its maximum speed at the lower end of its stroke where it strikes the tool I! as indicated at M and thereby transmits its kinetic energy to the tool.

It will be seen from Fig. 4 of the drawings and from the above description that in the portion of the cycle from A to E (Fig. 4) the energy derived from the driving motor is converted into kinetic energy of the piston l6 and cylinder ll in their upward acceleration and movement, and into potential energy represented by the compression of air in the chamber 8|. Between E and G the energy of the compressed air in chamber 8| is converted by expansion of the air into increased kinetic energy of the cylinder H. The kinetic energy of the cylinder is still further increased by the continued upward movement of the piston l6 against the resistance of the expanding air. In the phase between G and I the energy of the motor is utilized in accelerating the downward movement of the piston and in compressing the air in chamber 80 while the kinetic energy of the cylinder I1 is. also converted into potential energy of the compressed air. During the portion of the cycle from J to M,'the potential energy of the compressed air in chamber 88 is converted by complete expansion of the air into kinetic energy of the cylinder H. The kinetic energy of the cylinder is still further increased by the continued energy input represented by the movement of the piston l6 downwardly against the resistance of the air in chamber 88. At the instant of impact, shown at M in Fig. 4, the piston has reached the end of its downward stroke and the expansion of air in chamber 80 is completed. The energy input throughout the cycle has thus been converted into kinetic energy of the cylinder [1. The full utilization of the energy available to produce maximum velocity of the impact element H at the instant of impact results in the delivery of a highly eflective blow on the tool l9 and represents maximum efficiency in the cycle of operation.

The compression and expansion of the air in chambers 80 and 81 is approximately adiabatic,

outside atmosphere.

the temperature of the air being increased during compression and decreased during expansion.

cycle as pointed out above but also contributes.

to the cool running of the apparatus.

In order to obtain the greatest efliciency it is desirable that the speed of the motor, the radius of the orbital travel of the stud 51, and the weight of the piston and cylinder be so correlated that a resonant condition exists and the maximum transfer of energy takes place from the rotating stud 51 to the cylinder and tool. As will be seen from Fig. 4, the cylinder i1 lags behind the piston H5 in its movement throughout the cycle except at the moment of impact as illustrated at A and M when the cylinder and piston are both at the bottom of their respective strokes. By reason of the relative movement of the cylinder and piston, the stroke of the cylinder is substantially greater than that of the piston.

At the instant of impact as shown at M in Fig. 4 the piston and cylinder are in neutral relation to one another. I The piston is momentarily stationary, having reached the bottom of its stroke, and is substantially centered in the cylinder The air in chamber has been fully expanded and the compression of air in chamber 8| has not yet begun so that both chambers are substantially at atmospheric pressure and are preferably open to the atmosphere through the ends 15 and 16 of the slot 43 in the cylinder wall. This neutral relationship of the cylinder and piston at the instant of impact minimizes transmission of the shock of impact back through the piston and operating mechanism of the hammer and not only decreases wear and tear on the hammer itself but also reduces operator fatigue.

The slot 43 in the side wall of the cylinder I! not only accommodates the pin 48 by means of which the piston I6 is reciprocated but also serves the purpose of providing communication between the chambers 80 and 8| and the surrounding atmosphere when the ends of the slots are alternately uncovered by the piston. The large area passageways thus afiorded permits -free flow of air into and out of the cylinder and manner shown and described the effective area of both ends of the piston can be made the same and the need of packing or other devices to prevent leakage of air around a piston rod is avoided. A more compact arrangement of the device is made possible since the cylinder-which has a longer stroke than the piston-can project up beyond the crank pin 51 by means of which the piston is reciprocated.

As power hammers are frequently used in dustladen atmosphere, the chamber II of the casing N (Fig. 2) that contains the cylinder I'I, piston l6 and. driving mechanism is preferably completely closed so as substantially to exclude the By reason of the high emciency and cool running properties of the hammer in accordance with the present invention, such enclosure is possible without overheating. -It will be noted that the cylinder i1 is guided in its reciprocatory movement by the inwardly projecting tracks 35 and 38 (Fig. 3) and that the walls of 7 the chamber Ii are spaced a substantial distance from the cylinder so as to provide freedom of movement of the cylinder without appreciable resistance or damping by the air in the chamber I I. This contributes still further to the high eiliciency oi the apparatus. 3

Although the operating mechanism or the hammer is completely enclosed it is nevertheless readily accessible for inspection. By removing the cover plates l2 and 50 and the tool retainer l8 and unscrewing the bolt, allthe operating parts can be disassembled from the casing ii. The connecting rod ll, gear 84 and cross head I! with pin 48 come oil! with the cover plate l2 and motor is while the cylinder II can slide out through the open end or the casing.

Operation of the embodiment shown is a simple matter, as the same may be manually grasped by the handles 8 and s and the circuit irom an electricalconductor (not shown) may be closed to the motor it by the trigger switch I.

In view of the relatively high ei'ilciency or my device, no forced ventilation is required and overheating has not been encountered. Thus the relatively sealed unit isprotected from dust laden air.

I wish it to be understood that I do not desire to be limited to'the exact details or construction shown and described, for obvious modiilcations will occur to a person skilled in the art. It should be further understood that while an electric motor is illustrated in the drawings, my invention is not limited as to the type ot'motor or power source that is used to drive the hammer.

What I claim and desire to secure by Letters Patent is:

1. A power hammer comprising a cylinder closed at both ends and acting as a ram, guide means for removably supporting the cylinder for reciprocal movement, a double-ended piston slidably disposed within said cylinder, a rotary crank. a constant speed motor driving said crank, and connecting means between said crank and said piston, whereby rotary motion of the crank is transmitted to said piston to reciprocate the same.

2. A power hammer construction comprising a hollow.casing, a track in said casing, a hollow cylinder slidable along and guided by said track, with substantial space between the side walls of said cylinder and said casing, a piston slidable within said cylinder, rotary crank,'a

8 at both ends, a closed chamber enclosing said cylinder with substantial space between the side walls of the cylinder and the walls of the chambet, a track guiding said cylinder for reciprocation in said chamber, a piston in said cylinder. rotary power driven means ior reciprocating said piston and thereby imparting resonant reciprocatory movement to said cylinder by the compression of air alternately in opposite ends of the cylinder, said cylinder being ireely movable in L thespace inside the chamber substantially without damping.

5. A power driven hammer comprising a hollow cylindrical impact member closed at both ends to provide compression chambers at opposite ends of said member and having a slot in a side wall intermediate said compression chambers, means for guiding said cylinder for reciprocatory movement, a piston in said cylinder and power driven means extending through said slot ior reciprocating said piston and thereby transmitting reciprocatory movement to said cylinder by the compression of air alternately in said opposed compression chambers, opposite ends of said slotbeing alternately uncovered by said piston in its reciprocation to open said compression chambers alternately to the surrounding atmosphere.

6. A power driven hammer comprising a hollow cylindrical impact member closed at both ends to-provide compression chambers at opposite ends thereof, means ior guiding said cylinder for tree reciprocatory movement. a piston in said cylinder and power driven means for reciprocating said piston to transmit resonant reciprocatory movement to said cylinder solely by the compression and subsequent expansion of air alternately in said opposed compression chambers.

- I. A power driven hammer comprising a hol- 40 low cylindrical impact member having compresmotor for driving said crank and a connecting rod joining said crank and said piston, whereby rotary motion of the crank is transmitted to the piston to move the same in a reciprocatory manner and said piston acts to move said cylinder alternately in opposite directions by the compression of an elastic fluid disposed within the cylinder.

3. An electrically driven power hammer comprising a casing, a tool support connected to said casing, a tool movably mounted within said support, a pair of tracks in said casing, a cylinder having closed ends and a slot in a side wall thereof, said cylinder being slidable along said tracks with substantial space between the side walls of said cylinder and said casing, a piston slidable within said cylinder, a pin extending from said sion chambers at opposite ends thereof, the side wall of said cylinder being apertured intermediate said compression chambers to provide communication with the surrounding atmosphere, a tool, means for. holding said tool in position to be struck by said cylinder, a piston in said cylinder, said piston being of a length approximately equal to the distance between said compression chambers, and power driven means for reciprocating said piston and thereby transmitting resonant reciprooatory motion to said cylinder by the compression and subsequent expansion of air alternately in said 0pposed compression chambers to cause said cylinder to strike said tool, the relation and arrangement of the parts being such that the air in both of said chambers is substantially fully expanded at the instant of impact.

8. In a power driven impact tool, the combina- 5 tion with a casing and a tool. of a pair of recippiston through said slot, a movable stud, elecpiston alternately in opposite directions.

4. A power driven hammer comprising a hollow rocable elements comprising a cylinder having compression chambers at opposite ends thereof and an intermediate portion open to the surrounding atmosphere, and a double-ended piston operable in said cylinder, which elements are reciprocable in said casing and are also reciprocable relative to each other, a rotary crank. a motor for rotating said crank and means for connecting said crank with one of said elements to reciprocate said element to compress air alternately in said opposed compression chambers and thereby transmit energy to the other of said elements by the alternate compression and subsequent expansion of the air in said chambers to cy mp t member Substantially closed .7 cause said latter element to reciprocate in predetermined phase relation with said first element and to strike the tool at an instant when said first element is at the end of its stroke and substantially full expansion of the air in both of said compression chambers has occurred.

9. In a power driven impact tool, the combination with a casing, of a pair of reciprocable elements comprising a cylinder having compression chambers at opposite ends thereof and a longitudinal slot in the side wall of the cylinder extending between said chambers, and a doubleended piston reciprocable in said cylinder and having a length between opposite piston heads approximately equal to the length of said slot, means for guiding said cylinder for reciprocatory movement, and power driven means for reciprocating one of said elements and thereby transmitting reciprocatory movement to the other of said elements by the compression and subsequent expansion of air alternately in said opposed compression chambers, opposite ends of said slot being alternately uncovered by said piston to open said compression chambers alternately to the surrounding atmosphere.

10. In a power driven impact tool, the combination with a casing, of a pair of reciprocable elements comprising a cylinder having compression chambers at opposite ends thereof and an intermediate portion open to the surrounding atmosphere, and a double-ended piston reciprocabie in said cylinder, the inside length of the cylinder being substantially equal to the sum of the length of the piston between opposite piston heads and the combined length of the compression chambers, and power driven means for reciprocating one of said elements and thereby transmitting reciprocatory movement to the other of said elements by the compression and subsequent full expansion of air alternately in said opposed compression chambers.

ROBT. WORTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Scott Apr. 8, 1913 Number 

